The objectives of this project are to demonstrate that properly fractionated total-body irradiation can sterilize advanced lymphomas in mice and elucidate the variables in such a system. It has been demonstrated that lymphoma localized in the region of the thymus gland may be sterilized by upper thoracic irradiation. The dose needed is above the total body LD50/30 for mice. The limiting factor at such dose levels is damage to the bone marrow. Survival curves performed on mouse bone marrow yield a straight line dose-log survival after an initial shoulder. Recovery experiments indicate a complex recovery pattern with a maximum recovery of 25-30% at about 4-6 hours. In contrast, there is every indication that the dose-log survival curve for lymphoma cells is linear. Radiation fractionated every six hours would thus be expected to have the same effect as acute radiation on the lymphoma cells while allowing for recovery after each fraction in the bone marrow. Calculations indicate that such fractionation should eradicate the lymphoma while allowing adequate bone marrow survival compatible with the life of the animal. Independent tests of the effect of varying the size of the individual fractions and the time between these fractions will be carried out. Independent tests of the linearity of the lymphoma dose- log survival curve will be necessary, also. These data may then be used to predict the fractionation scheme necessary to achieve sterilization of the lymphoma while allowing survival of most of the mice. This system will then be used to attempt cure of advanced lymphomas by whole- body, fractionated irradiation.